First efforts at Silicone Molding - Assembled Coot!

Dave Diefenderfer

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I debated if I should put this on the monthly bench efforts, but thought maybe it could stand it's own thread....

I have 4 of the old Herters flat bottom coot decoys I got from John Livoti a few years back. I restle coated them and repainted them. I have since gotten another pr from John Bourbon, the newer, model 63 bodies.



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I prefer the old, smaller bodies with these heads. I want to round out my rig, and make up 8 more bodies, and need 6 more heads. Since I had a pr of heads not yet mounted, I thought I might try my hand at making a mold. A little reading, youtube watching, and questions, and I got started:




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I build a box with thin clear plastic from Home Depot. Because I had bought special, non-sulphur clay, I built up the area around the heads with corrugated plastic to take up space. It turns out, I likely had enough clay but oh well.

I filled the hole in decoy stems with hot glue and set them in the base. Worked the clay to the parting lines, and added registration dimples in the clay.
Release agent was sprayed into the cavity, and the Smooth-on Mold Star 30 was mixed and poured.



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After waiting the 6 hours of cure, I peeled open the box.



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And peeled off the mold half.



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After cleaning up the clay on the silicone mold half, I rebuilt the box and prepared for the other mold. Success!





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Today, I got to pour my first heads. I used Smooth-on Feather Lite, which is a 2 part Urethane casting resin, that is heavily filled. This material has a hardness of 58 Shore D, is machineable, supposed to be durable, and it floats. I the fill floats on the top and is quite hard. When you open the can it appears the material is fully cured. Once you break through the top half of each can, there is liquid below. After a good 10 minutes of mixing it all goes into solution.



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Mixed 1:1 by volume it has a pot life of about 8 minutes. Cure time is 2 hours.



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And finally I have the first heads out of the mold....



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I had calculated the volumes, but mixed a little extra to play it safe. After this first pour, I know my calculation was pretty spot on, and will not waste as much on subsequent pours.
I did get a little voiding at the base of the neck, that will easily be blended when I install the heads, but on the next pour I vibrated the mould after pouring to see if I might displace the bubbles? If these are the worst and all are the same, I am still pleased with this first molding attempt.



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What is not to love about a thread dedicated to coot decoys!

Whatcha planning for the bodies?
 
Unless I happen upon an original body to pull a mold from, I will try making them in pink foam.
 
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frank zampariello said:
Dave.... I have a 63 flat bottom Coot that I will bring to the LI Decoy Show.....might be just what you are looking for.

Yup, that is the body! See you Saturday.
 
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Outstanding!

After the cost of the mold materials, what do you think the cost per head is?
 
I have about $50 into the mold, though could have gone cheaper and some things (clay, release agent) will be used again and again. For the trial kit of Feather Lite, it was $25 I think, and hope to get 20 to 25 heads from it. I have 6 released, 2 poured this morning before work and hope to get 2 more pours this evening.... should be done by Wednesday with this can. All the literature talks about shelf life after initial exposure, but does not say how long? 6 days, 6 weeks, 6 months, IDK, but while I am making a mess, I will use it up. Between my needs, Brian's and Rufus, I am sure we will use up this first go. Then guys on FB have asked for some too. Not looking to make this a business, that will take the fun out of for me, but if I can help someone, I will within reason.
 
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After reading this and thinking about it a bit, I find it so refreshing that guys are able to do this on their own these days. Back in the day, you couldn't get any info on how to do it and everything was a trade secret (there were even some good forum fights about molding techniques in the olde days). Sure glad those days are gone and someone can just jump right in and produce a good product. Working with the silicone mold sure is neat, I enjoyed it when I built my lead anchor mold for my "H" anchors. I was too cost conscious and trying to get by with just enough made the process not nearly as it could have been. The cost of your components seems pretty darn good.

Again, very neat and thanks for sharing.

T
 
Dave, I use Smooth-On Smooth Cast, tinted with So-Strong black, which is rated at 72D for heads poured via a one piece mold made with Smooth-On Rebound 25. I make an initial pour to coat the entire head mold's interior and then allow it to settle into the bill and forehead area just as it begins to turn color and set-up, with the remainder of the head mold filled with 8lb density foam under the urethane skin. These heads last and repel most shot charges with minimal damage. I can't pour them as a solid unit, since they would be too heavy to balance-out with the decoy properly. I am assuming this is why you opted to go with feather-lite in a one part head. Have you played around with these to determine their durability?

I apply a thorough wash with lacquer thinner, followed by a Scotch-brite coarse pad rub-down, and another final lacquer thinner wash prior application of a urethane compatible primer will promote excellent paint adhesion. Not all primers are compatible with plastics...

Good luck!
 
Rick, this is my first attempts, and my first guess at materials. There is a Reynolds Advanced Materials shop in Orlando, near where I have been visiting my father frequently. Fun place to look around and get ideas. I took the coot heads and a Homer head to compare the material samples (they have pucks of each material available). I spoke to the staff, and read the literature and guessed at the materials I selected. All together I spent $77 there for a trial kit of the mold silicone, trial kit of the Feather Lite, some non-Sulphur clay, and release agent.

I bought the plastic for the boxes at Home Depot. Next time, the plastic will be thicker so it stays square, but that is only my OCD, it works fine bowed out!

I appreciate the input on how to prep the heads for paint... that is a concern. I have not been using release agent in the mold after the first pour, and the surface is much improved.

Since I will get my hands on an original body, I will do a brush on mold of that and do pour foam instead of carving I think. Will pick Tom Rowe's brain tonight, and follow some more youtube tutorials! The coot body is easy as it is flat bottomed! To make mixing foam more economical, I may make 2 molds to pour 2 at a time?
 
Ha ha, I only needed a few and wanted to learn some new skills! 2 at a time is not a way to be productive. More time setting up and cleaning up than anything... fine for a few, not production! Of coarse, since I am a process engineer, the wheels start turning....
 
Should we start a thread to name the 2018 Coot Travelling decoy now or wait awhile yet.

Very fun and interesting post. Did you put thought into the hardness of the foam and it being able to take 2 shot. How about the chosen mold release and”paint ability”. I’m sure this was all considered.

Mark
 
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Dave, here are the photos you requested, I can't PM photos:View attachment 010.JPGView attachment 011.JPGView attachment 012.JPG The sleeper redhead is made from a bird carved from Pat Godin's pattern book for that head display. I don't enjoy carving sleepers, but they are effective, so I made a mold off the last one made and poured some birds for my hunting partner and myself. This is what a mold looks like after twenty-six pours. The other mold is one I made for a pickleweed I carved off a photo of a Bob Furia bird he made with a palm frond. I used scrap balsa wood, so I ended-up making a mold off it to make forty or so more that were more resilient to routine use. This mold required me to cut a part line in the back to pop the head and bill out and rotate to remove, following curing, so I was forced to use Tom Rowe's technique of placing a fiberglass skin over it to keep the polyurethane skin and foam pours contained and maintain symmetry. I just used three spring clamps to hold it tight to its mate, rather than bolting them together like Tom does.

I am sure Tom told you that the first thin pour is the most important because it captures all the details of the plug master. I use Smooth-On thixotropic agent in a variety of drop dosages to thicken the silicone to ladle onto vertical surfaces near the end of pour(s) sequence to get the mold to a uniform thickness to escape having to use the fiberglass mold skin. If the foam pour volume is a little "off", I simply loosen the wingnuts at the front of the mold first, loosening the remaining two it it continues to expand.

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The bird with the two strap weights added as counterweights was a skin pour mistake that occurred via my leaving the mold sitting in the sun while mixing the polyurethane skin to pour. I allow the mixture to build into the head depression and then swirl the mold slowly to distribute a thin layer around the interior as the viscosity inreases, leaving an ever thickery layer behind. On this pour the batch set-up within a minute, resulting in a near solid head...why I am intrigued by your use of Smooth-On Featherlite. A solid piece of this is pretty dense, requiring the addition of the strap weight pieces to balance it out.
 
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